1. Field of the Invention
This invention relates generally to thermally conductive substrates used for disposing circuits thereon and more particularly to substrates having a layer of copper on which a dielectric layer adapted to to receive the circuit is disposed.
2. Brief Description of the Prior Art
Various electronic components, such as integrated circuits, tend to generate heat and can be damaged if subjected to excessive temperatures. A technique to mitigate harmful temperature excursions involves mounting such components and circuits on heat sinks of selected materials.
Certain materials such as Invar or molybdenum sandwiched between layers of copper have been found to be very useful in providing not only effective heat sinking characteristics but also in providing an effective thermal coefficient of expansion (TCE) match for components or layers mounted thereon. For some applications such substrates are subjected to high temperature air furnace environments during processing. For example, when thick film gold pads are provided for wire bonding of an IC, the gold is conventionally cured in an air environment. In order to prevent destructive oxidation of the copper during the high temperature excursion it is necessary to apply a protective layer on the copper. Nickel may be used for providing a protective coating which can be subjected to such elevated temperatures in air with negligible deleterious affects. However, a problem occurs in obtaining an adequate bond when forming a glass dielectric layer on the nickel in order to build a circuit on the substrate. The dielectric layer tends to peel away from the nickel making it unsuitable to mount a circuit.
It is therefore an object of the invention to provide a suitable bond between a glass type dielectric layer and a metal substrate. Another object is the provision of forming a glass type dielectric layer on a substrate having nickel coating thereon which layer is strongly adhered to the substrate to facilitate the building of circuits on the layer. Yet another object is the provision of articles having a copper layer to which is strongly adhered a glass type dielectric coating.